1. Field of the Invention
The present invention relates in general to emission control systems for an internal combustion engine, and particularly to an exhaust gas recirculation (EGR) system of the engine. More specifically, the present invention relates to an improvement in connecting an EGR valve or an EGR pipe to a plastic intake manifold of an internal combustion engine.
2. Description of the Prior Art
Hitherto, in motor vehicles powered by an internal combustion engine, an exhaust gas recirculation (EGR) system has been commonly installed for reducing NOx emissions produced by the engine. As is known, the EGR system is designed to recirculate a metered amount of exhaust gas into the air-fuel mixture in the combustion chambers to reduce the temperature in the combustion chambers and thus NOx emissions. In the EGR systems, an EGR valve is installed in an EGR passage for regulating the amount of EGR. Usually, the EGR valve is connected to an intake manifold of the engine. Under operation of the EGR system, the EGR valve which is constructed of a metal is highly heated by absorbing heat of the recirculating exhaust gas.
Thus, if the intake manifold is constructed of a plastic (viz., glass fiber-reinforced plastic) for reducing the weight of the engine system or for other reasons, it is necessary to take any measure for protecting the plastic intake manifold from the heat of the EGR valve.
Hitherto, various measures have been proposed and put into practical use for protection of the plastic intake manifold from the heat of the EGR valve, some of which are shown in Japanese Patent First Provisional Publications 5-256217 and 6-101587 and Japanese Utility Model First Provisional Publication 63-164554. In the Publication 5-256217, the EGR valve is mounted to the plastic intake manifold through a mounting bracket of corrugated stainless steel plate. In the Publication 6-101587, the EGR valve is connected to the plastic intake manifold with an interposal of a heat insulator therebetween, first bolts are used to secure the heat insulator to the manifold and second bolts are used to secure the valve to the heat insulator. In the publication 63-164554, a junction portion between the EGR valve and the plastic intake manifold is formed with an annular groove through which a coolant flows for cooling the junction portion.
In addition to the above-mentioned measures, a measure for protection of the plastic intake manifold from the heat of exhaust gas is described in Japanese Utility Model First Provisional Publication 1-102465. In this measure, a fresh air from an air cleaner is fed into an EGR pipe to reduce the temperature of the EGR gas led into the plastic intake manifold. Furthermore, for suppressing or minimizing direct contact of the highly heated exhaust gas with an inner wall of the plastic intake manifold, a leading end of the EGR pipe is projected into the interior of the intake manifold through a pipe passing opening formed in the same.